Resonator particle separator



3,093,733 RESONATOR PARTICLE SEPARATOR lohn P. Blewett, Bcllport, N.Y.,and John D. Kiesling,

River Edge, N.J., assignors to the United States of America asrepresented by the United States Atomic Energy Commission FiledJuly 8,1960, Ser. No. 41,708 3 Claims. (Cl. 250-41.9)

This invention relates to radiofrequency resonators and moreparticularly to resonators for exerting preferential forces on highenergy particles.

In high energy particle physics, it is often desirable to separateparticles of equal momentum but different mass and having energies onthe order of several billion electron volts. In the case of theparticles having energies of about one billion electron volts,relatively simple techniques are available for effecting the desiredseparation. But in the case of particles having about 10 BEV and greaterenergies, the problem heretofore has not been readily solvable.

Wave guide resonators have heretofore been considered for the separationof high energy particles; however, an inherent difiiculty with ordinarywave guide resonators is that they usually have field patterns whichinclude an associated magnetic field component normal to the axis and tothe transverse electric field. Because of the interaction of themagnetic and electrical fields in such a. wave guide resonator, wherebythe deflection caused by the transverse electric field is exactlycancelled by the deflection caused by the transverse magnetic field atthe required phase velocity, the electromagnetic waveguide, TE mode,cannot be operated in a travelling wave mode. Therefore, to obtain a netdeflection, the waveguide is operated very near cut and the transversemagnetic field is then negligibly small. Since the phase velocity forout off operation is greater than the particle velocity, the apparentphase velocity is reduced by the incorporation of drift tubes into thestructure. As a result, it is diflicult to realize an aperture greaterthan about a quarter wave length of the radiofrequency used to energizethe wave guide because of the restricting effect of the drift tubes.

This invention accomplishes the preferential deflection of high energyparticles in a wave guide resonator in which there is established fordeflection purposes, without the use of drift tubes, a field patternincluding a traveling wave of deflecting electric field free from theusual magnetic field component whose efliect, if present, would be tocancel the electric deflection. Separation of the particles isaccomplished by this traveling wave tranverse electric field. Thevelocity of the wave down the wave guide is chosen such that the desiredparticles gradually slip backward or forward along the deflecting wave.The length of the separator may be selected so that the total slipbetween these particles and the wave is exactly a full wave length. Thenet effect is that the desired particles spend equal times in fieldsdeflecting them in the two opposite directions and they emerge therefromwith their velocity parallel with the axis. At the same time, the wavevelocity has been chosen equal to that of an undesired particle type;thus the field continues to deflect that particle in one or the otherdirection throughout the length of the separator. Since particles arriveat all phases, both beams are fanned out with maximum intensity at theextremes of the deflection. On emergence, the desired particles from aparallel beam as compared to the undesired particles which have velocitycomponents away from the axis.

A wave guide resonator constructed to utilize the principles ofseparation described hereinabove, is shown in application Serial Number16,902, filed March 22, 1960,

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in the name of John P. Blewett which matured into Patent No. 3,016,458on January 9, 1963. In that arrangement, the boundary conditionsrequired in accordance with these principles are established by the useof a plurality of discrete, charged members arranged in parallel array.While quite satisfactory for carrying out the separation of theparticles as herein described, the present invention is an improvedversion in which there is provided a wave guide resonator of muchsimpler construction for the separation of the high energy particles. Aspointed out in the theoretical discussion and mathematical analysisforming the basis of this invention in the paper, A Radi0- FrequencyMass Separator for Complete Separation of High Energy Particle Beams byJ. P. Blewett, which appears in the Proceedings of the InternationalConference of High-Energy Accelerators and Instrumentation, Geneva,1959, pages 422-427, published by the European Organization for NuclearResearch, the resonator must establish a boundary condition defined byBy the instant invention these boundary conditions are established by aconstruction having the advantages of structural simplicity which arereadily translatable into lower construction costs. The improved waveguide resonator of the present invention can be fabricated convenientlyfrom an electrically conducting material such as copper and has the formof a rectangular wave guide resonator having transverse stubs disposedin repeating pattern as specifically to be described below. Such a waveguide is readily powered by conventional microwave techniques, and beingfully enclosed, does not radiate.

It is thus a first object of this invention to provide apparatus whichcan be used as a travelling wave structure for the preferentialdeflection of charged nuclear particle beams.

It is a further object of this invention to provide a resonator in whichprevious limitations in the use of such resonators to deflect highenergy particles are removed.

It is still a further object to provide a resonator which can be usedfor particle beam separation.

Still another object of this invention is to provide a wave guide ofsimple construction for the deflection of composite particle beams inwhich one species of particles having a particular velocity emergeswithout deflection and all other species of particles having velocitiesgreater or less than the preferred velocity experience deflection andemerge from the resonator with transverse velocity.

The exact nature of this invention as well as other objects andadvantages thereof will be readily apparent from consideration of thefollowing specification, relating to the accompanying drawing in which:

FIG. 1 shows preferred boundary conditions in accordance with thetheoretical principles involved in this invention;

FIG. 2 is a view along 2--2 of FIG. 1;

FIG. 3 shows an elevation view in section of a wave guide constructedinaccordance with the principles of this invention;

FIG. 4 is a top sectional view of an alternative embodiment;

FIG. 5 is a side sectional view of still another construction of a guidebuilt according to this invention; and

FIG. 6 is an embodiment similar to FIG. 3.

Referring to the drawing in which like numerals are used to identifylike parts throughout the several views, there is shown in FIGS. 1 and 2the ideal boundary shapes for a wave guide resonator satisfying Equation1 given above, in which y and z are the dimensions along theirrespective axes, a is chosen equal to w/c where w is 21rf and c is thevelocity of the unwanted particle.

This ideal shaping of a wave guide is described and developed in thepreviously mentioned publication. As noted in the earlier patentapplication, the structure utilizing bars to form the boundaryconditions shown in FIGS. 1 and 2 is satisfactory but many practicaldifiiculties are involved in the construction of that type of waveguide.

Referring to FIG. 3, there is in accordance with the principles of thisinvention shown 'a simplified rectangular wave guide 10 utilizinglateral stubs 12a, 1217, etc. for accomplishing the boundary shape shownin FIGS. 1 and 2 capable of providing the separation as hereinabovedescribed. Wave guide 10 supports a standingwave pattern which has thedesired traveling wave as one of its components provided the repeatlength L is such that ZL/Azv/czl where A is the imposed wave length andv is the velocity of the desired particle. This structure can alsosupport a simple travelling wave if properly terminated. As such it canbe described electrically as a microwave filter having a band pass inthe region of resonance as described herein.

The two regions A and B of FIG. 3 have slightly different crosssectional shapes so that the propagation constants Y and Y of the tworegions A and B, respectively, are different. The division is made sothat electric energy is stored principally in region A to deflect theparticles, and magnetic energy is stored in region B so that it will notdeflect the particles. If in region A the dimensions are such that theregion is near cut-off '(YEO) and the dimensions of region B are chosensuch that the region is above cut-off, a resonance can be obtained inthe structure for a field pattern that can be used to deflect a particlebeam.

A transmission-line solution can be obtained to describe this mode. Inregion A we can define propagation constant Y and a characteristicimpedance Z for a transverse electric (TE) mode such that In region Bfor propagation in the x direction -l"\-/J) Z'=w Zl7/Y where f' is-thecut-off frequency in region B.

From transmission line theory the resonance relation is approximatelywhich neglects the eifects of fringing fields at the junction of regionsA and B. Since Y is small and Yh is almost equal to 1r/2 we can writeand the resonance condition can be rewritten in the approximate form faAN (Th Typical solutions of Equation 9 are as follows:

f /f h/)\ b/)\ a'/)\ s/)\ k 0.954 0.275 0.1 0.1 0.4 0.5 0.950 0.2760.125 0.125 0.375 0.5 0.9995 0.289 0.125 0.125 0.375 0.5

In order to demonstrate how this invention is utilized to select thewave guide dimensions in a particular situation, consider the case whereit is desired to deflect 1r mesons travelling with anti-protons atparticle momenta of 6 b.e.v./c. The 1r mesons are moving at relativisticvelocities so that it is necessary to establish a travelling wave at thespeed of light to deflect the 1r mesons. With an excitation frequencyselected at 600 mc./sec. in order 'to obtain an overall wave guide ofreasonable dimensions (other frequencies may be selected for economic orotherpractioal considerations), the wave length A of the travelling waveto be established will be c/f where c is the speed of light, or 300 l06O0X10 =0.5 meter.

Substituting the values given in the second typical solution of Equation9 listed in the table above into Equation 9, values of h, b and d areobtained as follows:

h= 14.12 cm. b=6.25 cm. d: 12.5 cm.

For the overall length of the wave guide, Equation 3 in theabove-mentioned paper of J. P. Blewett may be utilized. In the abovecase, this is computed to be 36 meters.

Of course, it is understood that an alternate structure based upon theconfiguration of FIG. 3 to give better useful aperture can beconstructed by assembling two of the basic structures of FIG. 3 back toback and leaving out the common wall 13, as shown in FIG. 6. Stubs 12a,12b, etc, and 12a", 1212", etc. correspond to the stubs in FIG. 3 witha'pair of wave guides back to back as noted.

Alternate constructions to that shown in FIGS. 3 and 6 for carrying outthe principles of this invention are shown in FIGS. 4 and 5, whichembody techniques that may be used to shorten the length of region B(dimension h) to achieve a better mechanical design. The ridged guideresonator 10' of FIG. 4 provides the same f' /f =0.5 and utilizes ridges14 which partially fill the volume of stubs 12'. In FIG. 5 there isshown a step guide resonator 10" in which there will probably be low-:er power losses since current concentrations are not as high in thisgeometry as in the ordinary ridged guide of FIG. 4.

It is thus seen that there has been provided a waveguide structurecapable of separating high energy nuclear particles of different massesand equal momentum. The structure is relatively simple in shape andoffers greater flexibility in the use of wave guides for the separationof high energy nuclear particles as described above.

Thus it should be understood that the foregoing disclosure relates toonly preferred embodiments of the invention and that numerousmodifications or alterations may be made therein without departing fromthe spirit and scope of the invention as hereinafter defined by theappended claims.

We claim:

7 1. A TE mode wave guide standing wave resonator for removing anunwanted charged particle from a mixture of sub-atomic and nuclearparticles of equal momentum and different masses and velocities havingenergies of l b.e.v. and above passing through said resonator bydefleeting continuously the unwanted particle in the same directiontransverse to its path through said resonator comprising, conductivewalls forming a rectangular cross section along x and y mutuallyperpendicular axes and extending in length along a z axis perpendicularto said at and y axes, said particles travelling through said resonatorparallel to said z axis, stubs with rectangular crosssections spaced onone wall along the length of said resonator and extending out in lengthparallel to said y axis, said stubs spaced at a repeat length of M2where A is the free space wave length of the travelling wave componentof said standing wave moving in one direction down the length of saidresonator in the same direction as and at a velocity identical to thevelocity of said unwanted particle along its path in said resonator, andthe dimensions of said wave guide resonator being in accordance with therelation 4h Af (2s/x)(12s/x) 1 =1 f0 (211/x v 1 where h is the length ofsaid stubs, k is the ratio f /f f' is the cut-off frequency of saidstubs, f is the cut-off frequency of said wave guide, 1 is the frequencyof said standing wave, M is (f-f s is the distance between ReferencesCited in the file of this patent UNITED STATES PATENTS 2,514,779 MartinJuly 11, 1950 2,588,226 Fox Mar. 4, 1952 2,649,576 Lewis Aug. 18, 19532,712,069 Goldstein June 28, 1955 2,816,270 Lewis Dec. 10, 1957

1. A TE MODE WAVE GUIDE STANDING WAVE RESONATOR FOR REMOVING AN UNWANTEDCHARGED PARTICLE FROM A MIXTURE OF SUB-ATOMIC AND NUCLEAR PARTICLES OFEQUAL MOMENTUM AND DIFFERENT MASSES AND VELOCITIES HAVING ENERGIES OF 1B.E.V. AND ABOVE PASSING THROUGH SAID RESONATOR BY DEFLECTINGCONTINUOUSLY THE UNWANTED PARTICLE IN THE SAME DIRECTION TRANSVERSE TOITS PATH THROUGH SAID RESONATOR COMPRISING, CONDUCTIVE WALLS FORMING ARECTANGULAR CROSS SECTION ALONG X AND Y MUTUALLY PERPENDICULAR AXES ANDEXTENDING IN LENGTH ALONG A Z AXIS PERPENDICULAR TO SAID X AND Y AXES,SAID PARTICLES TRAVELLING THROUGH SAID RESONATOR PARALLEL TO SAID ZAXIS, STUBS WITH RECTANGULAR CROSSSECTIONS SPACED ON ONE WALL ALONG THELENGTH OF SAID RESONATOR AND EXTENDING OUT IN LENGTH PARALLEL TO SAID YAXIS, SAID STUBS SPACED AT A REPEAT LENGTH OF $/2 WHERE $ IS THE FREESPACE WAVE LENGTH OF THE TRAVELLING WAVE COMPONENT OF SAID STANDING WAVEMOVING IN ONE DIRECTION